yea, this came up a while ago. I'm guessing your phone has a rather big screen?

I did a bit of research back then and the app seems to decide which interface it uses according to your screen size. there seems to be no official way to change that. and I would strongly recommend not going any unofficial routes.

This forum is meant for technical support for PC and Mac. The technical support we can provide for Hearthstone on mobile devices is very limited; please see the Troubleshooting Hearthstone on Mobile Devices support article for more information.

You can also check the Bug Report forum to see if other players have reported the same issue.